A CCD type or CMOS type image sensor (solid-state image pickup device) generally used in the art includes a light receiving unit (an effective pixel area unit) which is constituted by a plurality of photoelectric conversion units that are arranged in a two dimensional array on a surface of a semiconductor substrate. An image signal of an object according to a light shape of the object funned at the light receiving unit is output from each photoelectric conversion unit. An optical black (OB) unit covered with a lightproof film is provided around the light receiving unit, and an offset component of the image signal of the object output from the light receiving unit is removed using a dark signal output from the OB unit as a reference signal.
That is, by subtracting a noise component in a state where light is not incident (which is output of OB unit), so called a dark output, from the image signal of the object (which is output of light receiving unit), a fine image signal of the object can be detected at the light receiving unit with high precision to accomplish a solid-state image pickup device with high S/N ratio. Since the dark output is changed due to a surrounding environment such as temperature, an image signal of the object with high S/N ratio can be obtained in all the environments by providing an OB pixel which is equal to an effective pixel and making the difference of the outputs thereof as the image signal of the object.
In the conventional CCD type or CMOS type solid-state image pickup device as described above, a photoelectric conversion unit (a photodiode) and a signal read-out circuit (an electric charge transmission path and an output amplifier for the CCD type, and a MOS transistor circuit for the CMOS type) which is used to output an image signal of the object detected from the photoelectric conversion unit to the outside should be formed on the same surface of a semiconductor substrate. For this reason, there is a problem in an aperture ratio in which an occupying ratio of the photoelectric conversion unit to a chip area of a solid-state image pickup device cannot become 100%. Such aperture ratio tends to become smaller than before recently according to the refinement of a pixel, and the lowering of the aperture ratio becomes a factor that reduces the S/N ratio.
As a result, a multilayer solid-state image pickup device having a structure in which a photoelectric conversion unit is not provided in a surface of a semiconductor substrate, only a signal read-out circuit is provided on the semiconductor substrate, and the photoelectric conversion layer is stacked at an upper side of the semiconductor substrate has drawn an attention.
For example, a solid-state image pickup device disclosed in Patent Document 1 is configured to detect an X ray or an electronic ray by a photoelectric converting using, for example, an amorphous silicon stacked at an upper side of the semiconductor substrate. In such solid-state image pickup device, an OB pixel is formed by stacking a lightproof layer of 2 μm thickness around an effective pixel area (a light receiving unit) of the outer surfaces of the solid-state image pickup device to shield the photoelectric conversion layer from light and detects a black level of the effective pixel.
A solid-state image pickup device disclosed in Patent Document 2 has a photoelectric conversion layer for detecting red, a photoelectric conversion layer for detecting green, and a photoelectric conversion layer for detecting blue, and captures the color image of an object. In such solid-state image pickup device, a lightproof film is stacked between the surface of a semiconductor substrate and the photoelectric conversion film at the lowest layer and light is not incident to a signal read-out circuit. The configuration of an OB unit is not specifically considered.
In addition, there is a solid-state image pickup device disclosed in Patent Documents 3 and 4 which is a multilayer solid-state image pickup device using a glass substrate or the like rather than a semiconductor substrate.
The solid-state image pickup device disclosed in Patent Document 3 has a configuration in which a photoelectric conversion film is stacked on a substrate formed with a TFT circuit. A pixel for removing noise is provided around an effective pixel, which is used to remove noise on the wirings or signal lines connected to the TFT circuit of the effective pixel. In Patent Document 3, the pixel for removing noise on the wirings or the signal lines is disclosed, but an OB pixel is not considered.
The solid-state image pickup device disclosed in Patent Document 4 has a configuration in which an OB pixel is provided for every effective pixel. The OB pixel includes a dummy capacitor having the same capacitance as the photoelectric conversion element included in the effective pixel and a TFT circuit having the same capacitance as the TFT circuit included in the effective pixel. In Patent Document 4, a configuration in which the dummy capacitor of the OB pixel and the photoelectric conversion element of the effective pixel are formed at the same layer, and a configuration in which the dummy capacitor of the OB pixel is formed below the photoelectric conversion element of the effective pixel, are disclosed as a configuration of the OB pixel and the effective pixel.